≡ Menu

Where Are the Jupiter Analogs?

Are Solar Systems like ours commonplace? One way of answering this is to look at the role of planets like Jupiter, which may have helped to determine the habitability of the inner planets. But worlds like Jupiter in orbits around 5 AU do not appear to be the norm, as Andrew LePage points out in this discussion of a new exoplanet find. LePage, publisher of an essential site on exoplanet detection (www.DrewExMachina.com) is also a Senior Project Scientist at Visidyne, Inc. in Boston. Today he shows us what we know and just how much we still need to clarify about the occurence of planets like Jupiter and their role in system habitability.

By Andrew J. LePage

Andrew_LePage_2014_small

A couple of decades ago, astronomers thought they had planetary systems figured out: they consisted of a more or less orderly set of worlds orbiting in the same plane with small rocky worlds close in and much larger, volatile-rich planets orbiting farther out beyond the “snow line” where plentiful water freezes into solid ice. Along with this model came the view among some that the presence of large Jupiter-like planets was not only likely but required to deliver water and clear out potential impact hazards to ensure the habitability of smaller rocky worlds orbiting inside a star’s habitable zone. Coupled with the Copernican principle that implies that there is nothing special about our Solar System, it was expected that extrasolar planetary systems would have similar architectures and possess “Jupiter analogs”.

But with the discovery of the first extrasolar planet orbiting a main sequence star back in 1995, this orderly view of planetary systems was called into question. This first exoplanet, 51 Pegasi b, was a Jupiter-mass world in a four-day orbit only 8 million kilometers from its sun. This “hot Jupiter” and a host of other extrasolar giant planets (EGPs) discovered since with a wide range of orbital radii clearly demonstrated that other arrangements of planetary systems are possible and that Jupiter analogs might not be the norm after all. Unfortunately, getting a clear picture of exoplanetary systems has been difficult because of the detection biases of the most often used detection techniques (i.e. precision radial velocity measurements and transit observations) clearly favor finding large planets in small orbits with short periods. But with two (and sometimes more) decades of data from various long-running radial velocity surveys now available for analysis, this is beginning to change as it now becomes possible to detect EGPs with orbital periods of a decade or more.

Earlier this month, the team responsible for Lick-Carnegie Exoplanet Survey announced the latest discovery of a Jupiter analog in a paper accepted for publication in The Astrophysical Journal. What makes this discovery all the more interesting is that the lead author, Dominick Rowan, is a senior at Byram Hills High School in Armonk, New York. Rowan recently won individual top honors in the Regional Finals of the Siemens Competition in Math, Science & Technology as a result of his work described in this paper. The newest Jupiter analog found by Rowan et al. orbits the Sun-like star HD 32963 about 120 light years away. With a mass estimated to be 94% that of the Sun, this star has a luminosity of about 90% of the Sun’s and an estimated age of around five billion years.

To find the new Jupiter analog, designated HD 32963b, a total of 199 radial velocity measurements acquired over 16 years using HIRES (High Resolution Echelle Spectrometer) on the 10-meter Keck I telescope at Mauna Kea, Hawaii were analyzed. These data were placed into two-hour bins to create 109 individual radial velocity measurements with a typical uncertainty of ±1.2 meters/second. A clear signal with a semiamplitude of 11 meters/second and a period of 6.49 years was seen in the data with only a 2×10-5 false alarm probability. This signal indicates the presence of a planet in a nearly circular 3.4 AU orbit – only a touch smaller than Jupiter’s 5.2 AU orbit around the Sun. Since the tilt of the new planet’s orbit with respect to the plane of the sky is not known, only the minimum mass or Mpsini of 0.70 times that of Jupiter (or MJ) can be determined using radial velocity measurements alone. By assuming a randomly oriented orbit, there is less than a one in three chance that HD 32963b is more massive than Jupiter.

Rowan et al. took their analysis one step further and examined the data from the Lick-Carnegie Exoplanet Survey to determine the occurrence rate of Jupiter analogs around Sun-like stars. For the purpose of this analysis, a Jupiter analog was defined as an EGP with a mass in the 0.3 to 3 MJ range orbiting a Sun-like star with an eccentricity less than 0.3 and a period of between 5 to 15 years (which corresponds roughly to orbital radii in the 3 to 6 AU range). The new find by Rowan et al. qualifies as a Jupiter analog by this definition.

jupiter_cassini

Image: Jupiter dominates our Solar System and may have had a role to play in the habitability of our own planet. We’re only now learning, however, how common such worlds are in orbits comparable to our own Jupiter’s at 5 AU. Credit: NASA/JPL/University of Arizona.

A review of the Exoplanet Data Explorer in August 2015 revealed 21 EGPs that met the working definition for Jupiter analog. Of these, eight published exoplanets that met the baseline requirements were found among the 1,120 Sun-like stars in the Lick-Carnegie Exoplanet Survey, yielding a raw frequency rate of 0.71%. In order to turn this raw number into a meaningful occurrence rate, the detection efficiency of the radial velocity survey for this class of planet must be taken into account. To accomplish that, Rowan et al. created synthetic radial velocity data sets for each star in their survey representing 320,000 different combinations of various planetary mass and orbital parameters. The ability of their analysis algorithms to detect these velocity variations through the noise in the data was then gauged to determine the detection efficiency.

The analysis by Rowan et al. found that the occurrence rate of Jupiter analogs orbiting Sun-like stars as defined here was approximately 3%. Making reasonable assumptions about the possible distribution of EGP properties, the rate can not be less than about 1% nor greater than around 4%. These results roughly agree with earlier studies based on microlensing and long-term radial velocity surveys. This suggests, contrary to earlier expectations, that Jupiter analogs are not common. This finding implies that either planet migration mechanisms from the snow line are very efficient at moving EGPs into smaller orbits or that EGPs have a difficult time forming at distances of about 5 AU.

But before the alarms are sounded by “rare Earth” advocates about the relative rarity of Jupiter analogs, it remains to be seen just how vital Jupiter analogs are to planetary habitability given the spectrum of architectures observed in exoplanet surveys to date. Even if Jupiter analogs prove to be required, current surveys have yet to search effectively for smaller Neptune to Saturn-size worlds at distances of about 5 AU or for EGPs at greater distances which may suffice as “Jupiter surrogates”. Only continued collection of radial velocity data along with new surveys, such as the current Gaia astrometry mission and the new generation of telescopes to image exoplanets directly, will allow us to fill in the missing pieces of our knowledge of exoplanetary systems. Thankfully this ongoing search provides opportunities for aspiring young scientists like Dominick Rowan.

The paper is Rowan et al. “The Lick-Carnegie Exoplanet Survey: HD32963 — A New Jupiter Analog Orbiting a Sun-like Star” accepted for publication in The Astrophysical Journal (preprint).

tzf_img_post

Comments on this entry are closed.

  • Terry Moseley December 18, 2015, 12:59

    It’s not surprising that we’ve found so few Jupiter analogs, as the orbits made them very hard to discover!
    1. The further the planet is from its parent star, the more exactly the plane of its orbit has to be tilted EXACTLY towards Earth for us to see transits.
    2. The further from the star, the longer the period, and so the longer the interval between transits: Jupiter’s period is almost 12 years, so you would need at least 36 years years to get unambiguous transit data for it.
    3. Also, the further from the star, the longer the period, so the longer it takes to get enough data to detect any wobble:
    4,. Finally, the further from the star, the less the wobble will be – the deviation from a stationary position follows an inverse square law.
    It’s a wonder we can detect any at all!

  • Steven Torry Rappolee December 18, 2015, 13:00

    I am a rare earth advocate I think so ring the alarm!
    never fear this is how science works.If we get a null result from SETI search for nearby areas of our galaxy then we can venture a guess as to why.So who knows yet for sure what happens in “every solar” system that does not have a late heavy bombardment?

  • andy December 18, 2015, 13:09

    The universe seems to conspire against the detection of Jupiter-analogues: their orbital periods are long enough that there is the potential for confusion with stellar activity cycles. Another paper about long-period giant planets reporting two such planets orbiting HD 95872 and ψ¹ Draconis B (note that ψ¹ Dra Bb has a higher eccentricity than the threshold in the Rowan et al. paper) also found that the long-period radial velocity variations of HD 10086 and β Virginis were actually caused by activity cycles.

  • Andrew LePage December 18, 2015, 13:12

    Readers who are interested in a broader comparison of the properties of our Solar System with other systems may be interested in the following review:

    http://www.drewexmachina.com/2015/08/15/how-typical-is-our-solar-system/

  • RobFlores December 18, 2015, 13:36

    So what lies in place of these Jupiter’s in the other 94% of sun like stars? Say at 4AU – 10AU Neptune type gas planets, or even pure Ice worlds
    such as Pluto and Eris.? it would be pretty shocking if a larger majority of cases there was NOTHING substantial other than a few small KBO type objects.
    I think among the weakest argument in the Rare Earth Hypothesis is the
    Need for a Jupiter like “vacuum cleaner’. Some studies have suggested
    that that Jupiter can DRAW IN hazzards to the Inner solar system as well as repel them. In contrast the Earth-Moon dynamic/implications is among the strongest argument in the RE hypothesis:

  • Brett December 18, 2015, 13:52

    This is one of those things where I’d really like to be able for us to detect Earth-size and smaller planets around sun-like stars down to about 2 AU out from their suns. We could then get a bead on how common “super-earths” are, how common those tightly packed systems are (and whether systems with Jupiter analogs have them), and so forth.

    Short Response: Arghh, we need better telescopes!

  • Jim Galasyn December 18, 2015, 14:24

    What’s the thinking on Nayakshin’s tidal downsizing model? It seems quite elegant to me, but I don’t know how much traction it’s getting. http://mnrasl.oxfordjournals.org/content/408/1/L36.short

  • FrankH December 18, 2015, 16:22

    Our own solar system shows signs of a “dance” between Jupiter and Saturn that affected all the outer planets. Other systems may have gas giants that careened through their inner system, disrupting or destroying any existing rocky planets or they could have been ejected or thrown into wider orbits that would show relatively small RVs.

    I’m also reminded of an early planetary system simulation, written by Stephen Dole in Icarus. Some models produced “pathological” massive planets close in to the star (depending on the initial mass function):

    Dole, Stephen H. “Computer Simulation of the Formation of Planetary Systems”. Icarus, vol 13, pp 494-508, 1970.

    and expanded by Richard Isaacman and Carl Sagain a few years latter:

    Isaacman, Richard. & Sagan, Carl. “Computer Simulation of Planetary Accretion Dynamics: Sensitivity to Initial Conditions”. Icarus, vol 31, p 510, 1977.

    Stephen Dole’s “Habitable Planets for Man” should be required reading by anyone interested in extra-solar planets. Even though it’s 51 years old, it’s well thought out: basic physics hasn’t changed in the last 50 years.

    In particular, Figure 21 would save a lot of bad PR and BS about “habitable planets”. He calculated a range of masses and radii that are exactly what the accepted values are now.

    The book is available for free (as a PDF):
    http://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf

  • Andrew Palfreyman December 18, 2015, 17:01

    The amazing variability in solar system compositions that we are just beginning to fully appreciate sends a clear message to our data analysis efforts – we need a very significant increase in our sample set size in order to begin to make appropriate generalisations and to see truly common patterns.

    So yes: telescopes, telescopes and more telescopes!

  • Brett December 18, 2015, 17:24

    Even if only Jupiter-analog systems had earth-like planets, and only 10% of those had habitable planets, you’d still have a pretty huge number of planets in the Milky Way like that. It’d be on the order of 40-ish million habitable planets in the Milky Way galaxy just from G-class stars.

  • RobFlores December 18, 2015, 18:15

    Yes, but if your estimate is correct at 40 millions or more potentially habitable worlds then Fermi rears its head.
    Because if life arises easily, then the galaxy would be Owned by someone.
    Since it is not then,
    Complex Life is incredible improbable OR;
    There is another factor reducing the number of habitable worlds by another order of magnitude (more like 4 million habitable worlds) at least.

  • Andrew LePage December 18, 2015, 18:24

    @Brett December 18, 2015 at 17:24

    You’re not all that far off. Extrapolating from a recent statistical analysis of Kepler finds suggests that maybe ~11% of Sun-like stars have roughly Earth-size planets in their HZ:

    http://www.drewexmachina.com/2015/11/03/the-prevalence-of-earth-size-planets-around-sun-like-stars/

    If we assume that the galaxy has ~400 billion stars, that ~20% of those stars are Sun-like G and K dwarfs, that ~11% of those have Earth-size planets in the HZ and that ~3% of those have Jupiter analogs (and that there is no correlation between Jupiter analogs and the occurrence rate of Earth twins), we could have ~264 million Earth-size planets in the HZ of Sun-like stars with Jupiter analogs present… just in the Milky Way alone. Still a pretty good size number! And if “Jupiter surrogates” of various sorts are sufficient for habitability (or if Jupiter analogs prove not to be needed at all), the number could be larger still.

  • Al Jackson December 18, 2015, 18:51

    Seems to me this is just more validation of the Copernican principle. Wheresoever we have supposed something special about our place in the universe or something distinct in our understanding of models of cosmogony it has always turned out to be wrong.
    I am glad the Stephen Dole book is mentioned , going down the Rare Earth anti-Copernican road is just as wrong as it was for the Roman Inquisition in 1616!

  • Enzo December 19, 2015, 5:50

    “For stars within a distance of approximately 150 light-years from the Sun, Gaia is expected to find every Jupiter-sized planet with an orbital period of 1.5 – 9 years.”

    http://sci.esa.int/gaia/28890-objectives/

  • Harold December 19, 2015, 13:37

    Kids these days with their big data and fancy algorithms! What is this world coming to when a high school student can expand humanity’s understanding of their place in the galaxy!

    @RobFlores December 18, 2015 at 18:15
    “Yes, but if your estimate is correct at 40 millions or more potentially habitable worlds then Fermi rears its head.
    Because if life arises easily, then the galaxy would be Owned by someone.
    Since it is not then,”

    What does an “owned” galaxy look like and do we have ability to detect the signs of an “owned” galaxy? From my perspective, SETI has demonstrated that there is a low probability of ETIs actively trying to maintain interstellar relations with Earth and a low probability of a galaxy populated by Dysonian ETIs. Couldn’t the Milky Way contain millions of star systems that are populated by ETIs without us having scientifically relevant evidence?

  • Eniac December 19, 2015, 17:29

    Harold:

    Couldn’t the Milky Way contain millions of star systems that are populated by ETIs without us having scientifically relevant evidence?

    No, it couldn’t. Not unless you assume that none of them ever venture beyond their own system. If there were millions, and some of them sometimes were to settle one of the 100s billion unpopulated systems, there would soon no longer be millions, but billions and more, until no more unpopulated systems are available. How would we notice that this had happened? We would ourselves be colonists, and we would know.

    Millions of ETI can only ever be a transient state lasting no more than a few million years, a blink of an eye compared with the age of the galaxy. It would be very unlikely to be happening right this moment. It hasn’t happened in the past, so at best it will happen in the future. Let’s hope that it will be our descendents making it happen.

  • Al Jackson December 19, 2015, 19:37

    “It hasn’t happened in the past, so at best it will happen in the future. Let’s hope that it will be our descendents making it happen.”

    I would never extrapolate the past of human history to predict the future of a high tech human civilization capable of star faring. Future human history , if it survives, as a High Civilization , has a horizon of predictability.

  • Harold December 19, 2015, 19:48

    Eniac,

    By millions of populated systems I do not mean millions of unique ETI species, I should have been clearer. I think ‘your’ hypothesis of galactic colonization relies on a model of expansion that has ETIs spreading as though they were a relentless computer program or an unintelligent bacterium colony in a petri dish. Suppose instead that intelligent technological species occur periodically with each new species colonizing a percentage of the galaxy. The Earth would need only to be within an uncolonized neighborhood of the galaxy.

    The notion that we are the first and have the opportunity to thoroughly colonize the Milky Way can certainly be attractive, but since we haven’t attempted to colonize the galaxy, our understanding of the mechanics involved is necessarily naive.

  • NS December 19, 2015, 22:46

    Re the “Copernican principle”, until we’ve a found lot more stellar systems and studied them in a lot more detail than we have now, we don’t know how unique the Earth is. The assumption of mediocrity is a good place to start but it’s really just playing the odds. It’s still possible that the Earth really is unique in some significant detail.

  • Eniac December 20, 2015, 1:19

    Harold:

    Suppose instead that intelligent technological species occur periodically with each new species colonizing a percentage of the galaxy.

    This is a very unrealistic supposition. What would the percentage be? If it were less than 100%, there would be a large number of colonies that have unpopulated systems right in their neighborhood. What do you suppose would keep such frontier colonies from colonizing those close-by unpopulated worlds? Some central government a hundred light years away? I think not. Unless you can come up with a plausible mechanism that universally prevents further colonization, that percentage you speak of will rise with time. I see no way for it to stop rising until it reaches 100%. Do you?

  • Eniac December 20, 2015, 1:31

    Al Jackson:

    I would never extrapolate the past of human history to predict the future of a high tech human civilization capable of star faring.

    I would not, either, and I don’t think I have. I am pointing out that it makes little sense to assume that high tech civilizations will change their attitude towards colonization suddenly, all worlds in unison, and stop doing it after some arbitrary percentage of occupancy is reached. The ways of ETI are much too unpredictable to allow such an assumption to be made. I’d go as far as saying it is a preposterous assumption.

  • PW December 20, 2015, 2:41

    Even with a Jupiter vacuum, the precious and so far, one of a kind Earth got smacked by something big enough to reboot life as we know it.
    Would the dino’s have evolved into space faring creatures? It’s impossible to know. By the time we are here, billions of years on earth have elapsed. The sun is much brightened, things have changed.
    I agree that the present exo planet discoveries are largely based on calculations that are biased to find Hot Jupiters. But yes, those are Hot Jupiters that absolutely NO ONE predicted. It’s shocking to me.
    We are at a critical phase right now of understanding the nature of planetary systems. Where is Carl Sagan when we need him the most? I grew up taught to believe we are nothing special. I hope that proves to be the case. Do I really have to revert to Rare Earth?
    Science is always the way forward. Observe and learn.

  • ole burde December 20, 2015, 4:52

    The only solid conklusion here , is that exoplanet astronomy have to get more funding , and that this funding have to be 100% locked on to the field without any possiblity for other pressure-groups or lobbyists to spread out the money across wider fields of general knowledge .
    Only in this way can we prevent other historically stronger branches of science to steel most of the cake …
    This is what is called ”building on sucess”
    Exoplanet astronomy is today one of the fastest advancing areas of knowledge , and as such it can be considered a kind of strategic ”breakthrough” which should be reinforced with all speed .
    This wil make more sense if we are willing to acept the mind- model of game theory , where the underlying asumption always includes an opponent .
    In our case the opponent is time itself , because even an optimist have to admit there are a million ways we could miss the Star-train …

  • Michael Simmons December 20, 2015, 20:36

    Given we don’t know all the factors that end up creating a close earth analog, it makes sense to look first at those systems that closely match ours. To me, that means looking for jupiter analogs around sun like stars and then hunting for other planets around them.

    Perfect example HD 13931b
    star is 1.020 solar masses.
    eccentricity 0.0200 at exactly the same distance from the star as Jupiter.
    And its mass is 1.88 Jupiter masses.
    Someone needs to do a much finer RV check on this system for other planets.

  • Eniac December 21, 2015, 0:02

    PW:

    Even with a Jupiter vacuum, the precious and so far, one of a kind Earth got smacked by something big enough to reboot life as we know it.

    Hardly. There was a “mass extinction”, i.e. a large number of species (17% of all families, 50% of all genera and 75% of all species) were lost in a shorter time than normal, but there were also plenty that remained. A setback, perhaps, but not a “reboot”.

    The dinosaurs, by the way, are still here. They evolved into birds. Some think atmospheric oxygen concentration, climate change, and the evolution of superior lungs have more to do with that then a meteor strike. After dinosaurs evolved the more efficient unidirectional respiratory system (perhaps driven by a reduction in atmospheric oxygen, which in turn was perhaps caused by the meteor impact), they became better adapted to the air, as breathing efficiency is critical to flight. Mammals, on the other hand, were better adapted to the land and cold temperatures. So each evolved into their separate niches, keeping each other out by competition. The “extinction of the dinosaurs” is a nice story, but it is a gross oversimplification of what actually happened. Not that we really know all that much about it….

  • Wojciech J December 21, 2015, 9:07

    “Because if life arises easily, then the galaxy would be Owned by someone.”
    There is no law of physics that demands that. In fact it could be argued that as civilization develops it would preserve unique biospheres and cultures purely out of self-interest(as they are great laboratory of biochemistry and technological and cultural development).
    With the possibility of engineering your own species as well, the need for constant reproduction diminishes as well.
    Eniac
    “Harold:
    Couldn’t the Milky Way contain millions of star systems that are populated by ETIs without us having scientifically relevant evidence?

    No, it couldn’t. Not unless you assume that none of them ever venture beyond their own system. ”
    Research and exploration is possible without extensive colonization. We explore and research Antarctica without extensive colonization of the landmass, as a example.

    “If there were millions, and some of them sometimes were to settle one of the 100s billion unpopulated systems, there would soon no longer be millions, but billions and more, until no more unpopulated systems are available”
    That assumes a very aggressively reproducing culture, which would be very strange for advanced technologically species with the mindset of colony of insects. It is rather likely that technological advancement reduces the need of reproduction as well as cultural growth leading to self-awareness as to animalistic motivations. With biological engineering which should be available to advanced species such needs are easily overcome(even with simple things as birth control, and we are not talking about cyborgization or uploading of minds).

    And of course if the first advanced civilization is conservative and motivated by preservation principles then it could easily safeguard against such very weird and unique swarm-like civilization.

    The fact that we don’t see our Galaxy or universe overwhelmingly colonized(unless we don’t see the obvious signs we mistake for natural objects) says that such civilizations don’t exist. Nothing more.

  • RobFlores December 21, 2015, 12:16

    What do we define as rare? 50,000 worlds in the entire galaxy that are
    like the Earth in composition and solar system makeup? Although this
    is far lower than 40 million. It can still answer Fermi. If 1% of those worlds have co-existing sentient technological life that would be 500 worlds
    (excluding the Core in all these calcs) that would be one civ per 4,000 LY.
    Would they detect each other? Maybe, Would they visit or last long enough
    to colonize their way to their closest neighbor? If not and somehow we ARE
    able to travel those distances, then we will find only their civilizational remains. But of course more likely we will be the fossil for others to find.
    This is why I lean to a very limited ETI in the universe, If many have fallen then we can too.

  • R Kelley December 21, 2015, 13:16

    I strongly suspect e that life may be common but intelligent life may be extremely rare (or almost non-existent other than on Earth). Reasons for this are as follows:
    1. If a 6-9 mile wide meteor had not hit the Yucatan peninsula and wiped out the Dinosaurs (worldwide) 66 million years ago, humans would have never evolved and there would not be intelligent life on Earth.
    2. If the Earth periodically went into a “snowball” state as it did prior to 600 million years ago, conditions would not have been favorable for the development of advanced (and intelligent) life on Earth. Since Earth is near the inner edge of our Sun’s habitable zone, I suspect that most habitable planets are further out in the habitable zone and will periodically slip in and out of a “snowball” state.
    3. As noted by an earlier writer, the moon has significantly slowed down the Earth’s rotation. If the rotation period of the Earth were only 12 hours, would climatic conditions have been stable enough over geologic time to promote the development of intelligent life?
    4. As noted by the great astronomer Geoff Marcy, the conditions that led to the development of man in east Africa may have been more a matter of chance than anything else.
    5. Since 80%-90% of the stars in the galaxy appear to be crowded near the galaxy’s core and subject to far more intense radiation, life may not be possible in the galactic center.
    6. I for one am still very pessimistic about the possibility of any life around planets in the habitable zone of M class stars given the tendency of such stars to have super-flares and the likelihood that planets in the habitable zone of such stars will be tidally locked and, as a result, lack a magnetic field.
    Even if intelligent life is very rare, I am personally hopeful that there will be many planets in the habitable zone of stars of spectral class F7-K2 that can be terraformed and made into comfortable Earths.

  • andy December 21, 2015, 14:33

    I’m also reminded of an early planetary system simulation, written by Stephen Dole in Icarus. Some models produced “pathological” massive planets close in to the star (depending on the initial mass function)

    Interestingly enough, there have been a couple of recent studies into the possibility of building hot and warm Jupiters in situ, as opposed to migrating them in from beyond the snowline.

    Boley, Contreras & Gladman (2015) “The In Situ Formation of Giant Planets at Short Orbital Periods

    Batygin, Bodenheimer & Laughlin (2015) “In Situ Formation and Dynamical Evolution of Hot Jupiter Systems

    The latter also addresses the question of where the neighbouring planets go in this scenario, also referencing the recent discovery that the WASP-47 system contains a super-Earth and a Neptune-mass planet in close proximity to an otherwise typical hot Jupiter.

  • Harold December 21, 2015, 14:38

    Hello Eniac and thank you for engaging.

    “Unless you can come up with a plausible mechanism that universally prevents further colonization, that percentage you speak of will rise with time. I see no way for it to stop rising until it reaches 100%. Do you?”

    I think cost benefit analysis would reveal some star systems are not worth colonizing. Using Earth islands as an analog for star systems, any technological species would have choices ranging from the Hawaiian islands through coral atolls that barely break the ocean’s surface. What would make a system qualify as a paradise would depend on the species. If a species experienced a persistent and high enough demand for expansion, at some point it would reach a point where conquest was as economical as new colonization. Personally, I don’t think a species would experience a persistently high demand for new colonies. What survival advantage would the 1,ooo,oo1th colony provide that the 1,000,000th didn’t? If we assume a colony collapse rate, it isn’t a huge stretch to imagine a stagnant growth rate of total colony count.

    As well, a galaxy that contains multiple unique species doesn’t require a stagnant growth rates, just growth rates that allow other species to grow as well.

  • Hiro December 21, 2015, 16:33

    I really fail to understand why we or any single species must colonize the entire galaxy. After achieving such feat, then would it be enough just to stay in this backward region? Why not colonizing M31 as well, then the next one is the whole Virgo supercluster right? The problem facing zero war during these expansions is some kind of delusional wish from my point of view.

  • Ronald December 21, 2015, 19:26

    Very interesting article by Mr. LePage and very relevant study by brilliant young Rowan! Almost a sequel to recent post Where to Look for Rocky Planets, https://www.centauri-dreams.org/?p=34599.
    So, the occurrence rate of Jupiter analogs around solartype stars is only about 3%.
    As others pointed out, and contrary to RE belief, a giant gas planet such as Jupiter is hardly or not useful as a protective vacuum cleaner.
    However, a Jupiter analog gas giant may serve another, much more important purpose in a medium-high metallicity system, such as our own, which hasn’t been mentioned here yet : to suck up most primordial dust from the proplyd, in doing so inhibiting the formation of the typical compact system of medium-sized planets (i.e. gas dwarfs (super-earths) and Neptune class planets) and allowing for the formation of small rocky planets, the true terrestrials, in the inner system.
    This crucial role of a Jupiter has been mentioned in studies of solar twins, such as in the excellent article by Asplund et al. that I mention in the Rocky Planets post.
    As I also mentioned in that post a really relevant question is whether small rocky planets can also form in (the HZ of) other planetary systems and metallicity regimes around solartype stars, in particular in the very common compact systems that apparently seem to be the planetary norm (e.g. 61 Virginis) and in very low metallicity systems exclusively consisting of small planets (e.g. Tau Ceti, 82 Eridani). If this is indeed the case, this would significantly increase the number of habitable planets.

  • Ronald December 21, 2015, 20:00

    With regard to Fermi, I tend to agree with Rob Flores and in particular R Kelley, and would like to elaborate that there may not be a real paradox, mainly an issue of relative rarity: remarkably, various studies, also mentioned on this website have come to estimates of several tens of millions to a few hundred million habitable terrestrial planets in our MW galaxy (more optimistic guesstimates of billions usually include a wider range of planet sizes and stellar spectral types).
    So, adopting the more conservative and realistic (?) estimates would leave us with, say, anything from 50 – 300 million orso habitable planets to begin with, the entire biochemical and evolutionary experiment, with all its hurdles from abiogenesis, via primordial (prokaryotic) life, higher (eukaryotic) cell, multicellular, specialized organs, sexual reproduction,…., to intelligence, and ultimately technological civilization. And each hurdle leaving a smaller subset. And then we know that intelligence need not result in technology that is able to communicate across the lightyears, and can even be extinguished again before it reacties that level, as the human Bottleneck also shows.
    Concludingly, I would suspect that life in the universe is probably very common, higher life relatively rare, intelligence very rare, and technological civilization exceedingly rare. We may very well be the only one at this moment in time in our MW galaxy.

  • Eniac December 21, 2015, 23:16

    I wish everyone would stop talking about expansion into the galaxy as if it was a deliberate interstellar collective decision, somehow. You are right, no-one is going to think: “We have only 1,000,000 worlds colonized, it is time for the 1,000,001st!”.

    More likely, this is the thought process: “There is this unpopulated system 4 light years from here, easily reachable the same way that our ancestors arrived here. It’ll allow our culture to survive, even if some great catastrophy were to destroy this here, our only home. Besides, the Kyrellians in the East and the Travonians towards the Center may have their eyes on this one, too, so we better hurry.”

    And while this thinking may not occur on all worlds, or even many, it is hard for me to believe that it would not at least occur on some. Especially since we have already allowed for it to have happened in the past. It takes only a few such decisions, and a moderately long time, to fill the galaxy without anyone ever intending to.

  • Eniac December 21, 2015, 23:51

    R Kelly:

    Some of your reasons for believing that intelligent life is rare while life itself maybe common have logical flaws in them:

    1. If a 6-9 mile wide meteor had not hit the Yucatan peninsula and wiped out the Dinosaurs (worldwide) 66 million years ago, humans would have never evolved and there would not be intelligent life on Earth.

    A later impact could have done it, they are not that uncommon. Or, non-humans could have evolved intelligence.

    2. If the Earth periodically went into a “snowball” state as it did prior to 600 million years ago, conditions would not have been favorable for the development of advanced (and intelligent) life on Earth. Since Earth is near the inner edge of our Sun’s habitable zone, I suspect that most habitable planets are further out in the habitable zone and will periodically slip in and out of a “snowball” state.

    There are equal numbers of planets both closer or further from Earth, so wherever you put your redefined zone of habitability you’ll find planets there. You can speculate that this zone is very narrow, but it would be just that, speculation, without real evidence.

    3. As noted by an earlier writer, the moon has significantly slowed down the Earth’s rotation. If the rotation period of the Earth were only 12 hours, would climatic conditions have been stable enough over geologic time to promote the development of intelligent life?

    Yes, of course, why not?

    4. As noted by the great astronomer Geoff Marcy, the conditions that led to the development of man in east Africa may have been more a matter of chance than anything else.

    A matter of chance, sure. But how does that imply unlikely? If not Africa, maybe somewhere else? If not then, maybe some other time? There were plenty of pre-human primate species around, and in the longer view we do not have to restrict ourselves to primates, either.

    5. Since 80%-90% of the stars in the galaxy appear to be crowded near the galaxy’s core and subject to far more intense radiation, life may not be possible in the galactic center.

    What radiation? Cosmic rays? Those don’t penetrate the atmosphere, and nobody knows if they are any more intense near the center of the galaxy than here.

    6. I for one am still very pessimistic about the possibility of any life around planets in the habitable zone of M class stars given the tendency of such stars to have super-flares and the likelihood that planets in the habitable zone of such stars will be tidally locked and, as a result, lack a magnetic field.

    Neither flares, not tidal lock, nor lack of magnetic field are known to be detrimental to the development of intelligent life. A larger planet and/or a thicker atmosphere can arguably take care of all of them.

  • Eniac December 22, 2015, 0:23

    Ronald:

    Concludingly, I would suspect that life in the universe is probably very common, …

    I don’t think you have actually mentioned the evidence on which you base this first one of your conclusions. Do you have any indications that life arises out of sterile geochemistry this easily?

  • Wojciech J December 22, 2015, 10:05

    Eniac
    “More likely, this is the thought process: “More likely, this is the thought process: “There is this unpopulated system 4 light years from here, easily reachable the same way that our ancestors arrived here. It’ll allow our culture to survive, even if some great catastrophy were to destroy this here, our only home. Besides, the Kyrellians in the East and the Travonians towards the Center may have their eyes on this one, too, so we better hurry.”
    I doubt that entities advanced thousands of years ahead of us will stay in unchanged biological form, we ourselves at this stage are starting to tinker with changing both our biological nature and adjusting it with technological devices.
    For a digital, biologically immortal or post-biological entities the desire for population growth wouldn’t be on top of priorities.
    Nor would I believe that concepts such as nations or tribes would be of interest to such entities and probably would be seen as we see ant hives competing to gain control of sugar cubes left from our picnic on the grass.

    As to preserving your culture-there are better ways of doing it than constant reproduction-isolated red dwarfs on outskirt of galaxy, black holes and so on.

    “It takes only a few such decisions, and a moderately long time, to fill the galaxy without anyone ever intending to.”
    Our observations show that such civilizations do not exist in visible universe(unless we are missing some obvious sign we take for natural). Their non-existence doesn’t exclude possibility of other non-aggressively colonizing civilizations.

  • Ronald December 22, 2015, 11:34

    Eniac December 22, 2015 at 0:23;
    You are right, I did not offer actual evidence for my first assertion, however, the essence of my argumentation is that *each next step in the process leaves a smaller subset*. Hence, increasing relative rarity in the course of the evolutionary process.
    And with regard to (relative) commonness of primitive (singe-celled, prokaryotic) life: it arose very early in earth’s history, whereas Eukaryotic life, multicelled life and and specialized organs took much longer. This may have had to do with the oxygen content of our atmosphere (today’s post!).

  • Eniac December 22, 2015, 22:22

    Wojciech J: It seems you misunderstood pretty much everything I said. I’ll try one more time to clarify:

    I doubt that entities advanced thousands of years ahead of us will stay in unchanged biological form, we ourselves at this stage are starting to tinker with changing both our biological nature and adjusting it with technological devices.

    I completely agree with you. All I am willing to assume is that some kind of logical thinking is going on, and some sort of motivation to preserve one’s culture.

    For a digital, biologically immortal or post-biological entities the desire for population growth wouldn’t be on top of priorities.

    I have not mentioned population growth. Population growth cannot be addressed by colonization, nor is it the point of it.

    Nor would I believe that concepts such as nations or tribes would be of interest to such entities and probably would be seen as we see ant hives competing to gain control of sugar cubes left from our picnic on the grass.

    Also not one of my assumptions. I do expect, though, that civilizations on different star systems will be separate entities, and think of each other as us and them, despite being related by descent. Interstellar communication delays pretty much guarantee that. This is not strictly necessary for my argument, though.

    As to preserving your culture-there are better ways of doing it than constant reproduction-isolated red dwarfs on outskirt of galaxy, black holes and so on.

    I have not advocated “constant reproduction”. There is no better way to preserve one’s culture against system-wide catastrophe than settling the next star system. Black holes or the outskirts of the galaxy are simply too far away. How can they possibly be better?

    “It takes only a few such decisions, and a moderately long time, to fill the galaxy without anyone ever intending to.”
    Our observations show that such civilizations do not exist in visible universe(unless we are missing some obvious sign we take for natural). Their non-existence doesn’t exclude possibility of other non-aggressively colonizing civilizations.

    What I have described is non-aggressive colonization. You are supposing a million civilized systems that never, ever settle neighboring unoccupied systems. It is true that this is a possible explanation for the Fermi “paradox”. To me, though, it seems unrealistic and contrived, when the simple assumption of extremely rare abiogenesis makes so much more sense.

  • Eniac December 22, 2015, 22:42

    @Ronald

    *each next step in the process leaves a smaller subset*

    This is quite obviously true, but we are interested in why the end result is so very small. It could be that one of those factors is extremely small and the others fairly large, or they could all be small. You have stated an opinion on that without any evidence backing it up.

    In my opinion, all the factors after abiogenesis are comparably large, and they do not form a single linear chain, but rather a huge network of many alternate paths. My evidence is the apparent power of persistence that allows evolution to make life succeed practically everywhere on Earth. Abiogenesis is the last step that is not a result of evolution, but random chance, instead.

    Knowing life is here, now (which we are sure of), we would statistically expect it to have started early. Otherwise, there would not have been enough time to develop to the point where it is now. Evolution works great, but it very, very slow. For this reason, an early beginning is not evidence for a high prior probability (stat speak for the original probability that is unbiased by hindsight).

  • Ronald December 23, 2015, 19:32

    Eniac December 22, 2015 at 22:42
    “In my opinion, all the factors after abiogenesis are comparably large”
    “Abiogenesis is the last step that is not a result of evolution, but random chance, instead.”

    Ok, if I understand you right, you say that abiogenesis is very uncertain, chance and probably very small chance. And that after that everything looks pretty certain.

    I disagree:
    First of all abiogenesis being pure random chance is a completely unfounded assertion, we simply know too little about it. However, it seems likely that some kind of gradual molecular/biochemical evolution (e.g. prion like proteins, RNA) also took place there.

    Secondly, or rather in the first place it seems odd to me that you consider all evolutionary steps after abiogenesis ‘comparably large’, clearly this is not the case: for the vast majority of time there was prokaryotic life, then also eukaryotic single-celled, complex multicellular came relatively late.
    Also see my and other comments under today’s post about the Great Oxygenation.

    But ok, let me rephrase myself: Concludingly, I would suspect that primitive, prokaryotic life in the universe is probably very common in comparison with complex multicellular life.

  • Harold December 24, 2015, 11:23

    @Eniac
    “Population growth cannot be addressed by colonization, nor is it the point of it.” Eniac

    I wholeheartedly agree. Population growth may reinforce the desire for colonization, but colonization will never solve overpopulation. Overpopulation would need to be solved in situ.

    “I do expect, though, that civilizations on different star systems will be separate entities, and think of each other as us and them, despite being related by descent. Interstellar communication delays pretty much guarantee that.” Eniac

    Again I agree with you. I would also add genetic and technological divergence to cultural divergence. The greater the difference between systems, the more likely divergence is to occur and at an increased rate.
    That being said, doesn’t that logic counter-indicate:

    “There is no better way to preserve one’s culture against system-wide catastrophe than settling the next star system. ” Eniac

    Personally, I think colonization increases diversity and after a relatively short time frame (a fraction of the time required for 100% colonization) the civilizations that are interested in preserving their culture will be very selective about where they colonize.

  • Eniac December 25, 2015, 22:48

    Harold

    That being said, doesn’t that logic counter-indicate:

    “There is no better way to preserve one’s culture against system-wide catastrophe than settling the next star system. ” Eniac

    Not really. Even if great diversification can be expected in the future, this will not reduce the appeal of colonization. At the point of colonization, the two cultures that may develop much different in the future, are still the same. The British or Spanish would not have been deterred by the prospect that their colonies would one day rebel against the motherland and become independent, or do you think so?

    About being selective about where to colonize: Once is enough. “Where” will be one of the closest unoccupied systems, probably all of them, over time. Unless our far descendents still prefer planets: Then they might be “selective” and look for something “Earth-like”. I would not bet on this.

  • Eniac December 25, 2015, 22:57

    Personally, I think colonization increases diversity and after a relatively short time frame (a fraction of the time required for 100% colonization) the civilizations that are interested in preserving their culture will be very selective about where they colonize.

    Why do you think the diversity among other colonies (“them”) would influence a particular civilization’s (“us”) motivation to get into that yet unoccupied system nearby? I would think the awareness of diverse potential competitors would heighten, rather than dampen, that motivation.